Could be when you receive a call that it changes from stereo mode to hands free mode.
I’m on iOS, so not sure I can provide a specific solution… however I can try a call later today and see if have similar with my air 2 pros.
Only other thing I can think of, not knowing android devices well, is if you have a setting for balance somewhere in your phone for calls?
Otherwise they work well for music and non call application?
I’ll edit in the reply towards the end of day today.
I tried a couple calls with both earbuds in, and call sounded centred.
So I wonder if your balance on your phone maybe shifted in the sound settings?
Otherwise, might be good idea to send of a request to service.